Transverse sealer for packaging machine

ABSTRACT

A transverse sealer for a packaging machine has a pair of seal jaws for sealing a film after it is made into the shape of a bag by a former and the bag is filled with articles to be packaged. The pair of seal jaws are disposed on opposite sides of the path of the film and downstream to the former. A pair of rotary arms supporting these seal jaws is moved towards and away from each other such that the seal jaws move in straight trajectories along the path of the film and is so controlled that the compressive force between the seal jaws can be maintained at a specified level according to the thickness and material property of the film.

BACKGROUND OF THE INVENTION

This invention relates to a transverse thermal sealer for sealing apackaging material used in a packaging machine for concurrently fillinga bag with articles such as foods and making a packaged product.

A bag-making packaging machine for concurrently forming a bag, fillingit with articles such as foods and making it into a packaged product,such as a so-called pillow-type packaging machine, is adapted to sealthe mutually superposed longitudinal side edges of a belt-like elongatedpackaging material (hereinafter referred to as a film) while this filmis being transformed into the shape of a bag by means of a former, andto thereafter transversely seal the bottom of the film, while thetubularly formed film is being pulled, by means of a pair of transversethermal sealing means disposed below the outlet of the filling cylinderused for filling the tubular film with articles to be packaged. Sincesuch a packaging machine is capable of simultaneously and continuouslyforming bags and filling them with articles to be packaged, it isconsidered an apparatus with high workability.

Japanese Patent Publication Tokkai 235006/87 disclosed an apparatus ofthe so-called rotary driving type adapted to cause the heating surfacesof its transverse sealing means to contact the film while the transversesealing means are moved linearly in the direction in which the film isbeing pulled, such that a sufficiently long time can be spent for thetransverse sealing process even if the period of cyclic packagingoperation is shortened. For the purpose of causing the transversesealing means to move in a linear trajectory, however, this apparatusmakes use of D-shaped grooves to guide these means, while causing themto undergo a cyclic motion. In other words, their linear trajectory andthe compressive force between them are uniquely determined, and the filmmay be subjected to an unreasonable force from them, depending on thethickness, material property and/or width of the film. As a result, thefilm may be damaged, or the apparatus may fail to reliably perform atransverse sealing process.

Packaging machines of the so-called intermittent driving type are alsoknown. They are structurally simpler, although disadvantageous from thepoint of view of reducing the period of cyclic motion, and arecharacterized as pulling the film intermittently and carrying out thetransverse sealing while the film is stopped. The method of using ahydraulic (oil-pressure) cylinder has been known in this connection forcompressing the transverse sealing means against each other andadjusting the compressive force between them by controlling thispressure cylinder. Such a cylinder, however, tends to make the apparatusbigger as a whole, and there arises the problem of keeping the oil forthe cylinder away from the articles to be packaged.

The present invention has been accomplished in view of these problems,and its first object is to provide a transverse sealer for a packagingmachine of the rotary driving type (rotating type) capable of adjustingthe compressive force between its transverse sealing means to a setlevel according to the thickness, material property and width of thefilm.

A second object of the invention is to eliminate the hydraulic cylinderfrom a packaging machine of the intermittent driving type such that thepackaging machine can be made compact and the contamination by oil ofarticles to be packaged can be prevented.

SUMMARY OF THE INVENTION

A transverse sealer according to the present invention for a packagingmachine, with which the first object mentioned above can beaccomplished, functions to form a belt-like film into the shape of a bagand to seal it transversely to the direction of motion of the film afterit is filled with articles to be packaged, and comprises a pair oftransverse sealing means disposed opposite to each other across the pathof the film and on the downstream side of a bag-forming means fortransforming the film into a specified shape for forming a bag, a pairof rotary driving means for causing this pair of transverse sealingmeans to rotate in synchronism with and near each other in the samedirection as that of the motion of the film, and atrajectory-compression adjusting means for not only causing the pair oftransverse sealing means to move in a linear trajectory along theaforementioned path of the film by moving the rotary driving means awayfrom or towards each other, but also maintaining the compressive forcebetween the transverse sealing means at a specified level, while thefilm is being sandwiched between the transverse sealing means by therotary driving means. With a transverse sealer thus structured, thetrajectory-compression adjusting means causes the pair of transversesealing means to move in a linear trajectory along the path of the filmand maintains the compressive force therebetween to a desired level suchthat the film, which is being supplied continuously, can be dependablysealed in the transverse direction according to the thickness, materialproperty and width of the film.

According to a preferred embodiment of the invention, there is alsoprovided a stroke adjusting means for adjusting the distance of strokeby the transverse sealing means along the linear portion of theirtrajectory. In other words, a distance of stroke, or a sealing time,appropriate for the thickness, material property and width of the filmcan be selected for a suitable transverse sealing of the film.

According to another preferred embodiment of the invention, thetrajectory-compression adjusting means is disposed so as to be movablein the direction in which the pair of transverse sealing means movesaway from or towards each other. It comprises a pair of mobile framessupporting individually the pair of rotary driving means for receivingthe reaction from the force of compression, a linear-to-rotary motionconversion means for converting the relative motion between the mobileframes due to the aforementioned reaction into a rotary motion, aseparation-controlling motor for causing the pair of mobile frames tomove in the aforementioned direction of motion away from or towards eachother through this motion conversion means, and a control means fordriving this separation-controlling motor at a constant set torque suchthat the pair of transverse sealing means can move in a specifiedtrajectory including a linear section. With such a structure, thecompressive force can be maintained at a level corresponding to thetorque set for the separation-controlling motor. Since thetrajectory-compression adjusting means has both the function of movingthe pair of transverse sealing means in a desired trajectory and thefunction of maintaining the compression therebetween at a constantlevel, the structure of the machine as a whole can be made simpler thanif these two functions are performed by two separate mechanisms. Since amotor is used instead of a hydraulic cylinder, furthermore, theapparatus can be made more compact and the possibility of contaminationby oil is also eliminated.

According to still another preferred embodiment of the invention, thepair of mobile frames, the separation-controlling motor and the controlmeans, of which the trajectory-compression adjusting means is comprised,also serve as parts of the stroke adjusting means. This additionallycontributes to the reduction in size of the machine.

The stroke adjusting means may be structured differently, with ashifting means for shifting the pair of rotary driving means by a setdistance in the direction of travel of the film when the transversesealing means return to their starting positions for the sealing. With astructure like this, the control becomes easier because the pair oftransverse sealing means follows a simple trajectory which is acombination of a straight line and a semicircular arc. This shiftingmeans may be set so as to be movable in the direction of motion of thefilm and provided with a shifting frame for supporting the pair ofrotary driving means and a longitudinal shift motor for moving thisshifting frame in the same direction of motion. With this structure,too, the apparatus can be made compact and contamination by oil can beprevented because use is made of a motor instead of a hydrauliccylinder.

According to a further preferred embodiment of the present invention,there is also provided an acceleration-deceleration mode setting meansfor causing the pair of rotary driving means to gradually separate fromeach other before the transverse sealing means reach starting positionsfor sealing and to gradually move toward each other after the transversesealing means reach their end positions of sealing. This contributes toa smooth movement of the transverse sealing mechanism because suddenmotion of the rotary driving means at the starting and end positions forsealing can be eliminated.

According to a still further preferred embodiment of the invention, eachof the transverse sealing means has a stripping plate and thetrajectory-compression adjusting means includes a stripping mode settingmeans for setting the trajectory of the transverse sealing means suchthat the stripping plates will stroke the surfaces of the film prior tothe sealing process in order to prevent the articles to be packaged frombecoming trapped inside the sealed section of the film. This embodimentcontributes to a dependable sealing by eliminating the possibility ofarticles getting trapped between the sealing surfaces.

According to still another preferred embodiment of the invention, atleast one of the pair of transverse sealing means is provided with areturning means for pushing it towards the other of the transversesealing means by an elastic restoring force proportional todisplacement. With the returning means thus provided, the transversesealing means, to which it is provided, can return to its normalposition when it becomes sloped with respect to the other such that thedistance between them changes. In this manner, pressure can be applieduniformly to the film from one position to another between the pair oftransverse sealing means.

A transverse sealer according to the present invention for a packagingmachine, with which the second object mentioned above can beaccomplished, comprises a pair of transverse sealing means disposedopposite to each other across the path of the film and on the downstreamside of a bag-forming means for transforming the film into a specifiedshape for forming a bag, and a compression adjusting means for not onlycausing the pair of transverse sealing means to move towards or awayfrom each other so as to be able to sandwich a specified sealing area ofthe film between them for sealing, but also maintaining the compressiveforce between the transverse sealing means at a specified level. Thecompression adjusting means is disposed so as to be movable in thedirection in which the pair of transverse sealing means moves away fromor towards each other, and comprises a pair of mobile frames forsupporting individually the pair of transverse sealing means andreceiving the reaction of the force of compression, a linear-to-rotarymotion conversion means for converting the relative motion between themobile frames due to the aforementioned reaction into a rotary motion,and a separation-controlling motor for causing the pair of mobile framesto move in the aforementioned direction of motion away from or towardseach other through this motion conversion means.

When a packaging machine of the intermittent driving type thusstructured is used for thermal sealing while the film is stopped, thecompressive force between the pair of transverse sealing means ismaintained at a specified level. Thus, the machine can carry outtransverse thermal sealing appropriately according to the thickness,material property and width of the film. Since a motor is used insteadof a hydraulic cylinder, furthermore, the machine can be made compactand the problem of contamination of the articles to be packaged by oilcan also be eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagonal view of a pillow-type packaging machine with atransverse sealer according to a first embodiment of the presentinvention.

FIG. 2 is a frontal sectional view of the arm rotation mechanism of thesealer of FIG. 1.

FIG. 3 is a structural diagram showing the mechanism for moving the axisof the arm in the sealer of FIG. 1.

FIG. 4 is a block diagram of an example of operation control for thesealer of FIG. 1.

FIGS. 5a and 5b are timing diagrams for the basic transverse sealingmode of operation of the sealer of FIG. 1.

FIGS. 6a and 6b are timing diagrams for the end acceleration mode oftransverse sealing operation of the sealer of FIG. 1.

FIGS. 7a and 7b are timing diagrams for the transverse mode of operationwith stripping by the sealer of FIG. 1.

FIGS. 8a and 8b are timing diagrams for the end acceleration mode oftransverse sealing operation with stripping by the sealer of FIG. 1.

FIG. 9 is a frontal sectional view of an essential portion of atransverse sealing mechanism according to a second embodiment of thepresent invention.

FIG. 10 is a diagram for showing the principles of the transversesealing mechanism of FIG. 9.

FIG. 11 is a schematic structural diagram showing the structure oftransverse seal jaw which is a variation on the second embodiment of theinvention.

FIG. 12 is a schematic structural diagram showing the structure oftransverse seal jaw which is another variation on the second embodimentof the invention.

FIG. 13 is a schematic structural diagram showing a transverse sealingmechanism according to a third embodiment of the invention.

FIG. 14 is a diagonal view of a packaging machine with a transversesealer according to a fourth embodiment of the invention.

FIG. 15 is a block diagram of an example of operation control device forthe mechanism of FIG. 14.

FIG. 16 is an action-timing diagram for the mechanism of FIG. 14.

FIG. 17 is a plan view of an essential portion of a device according toa fifth embodiment of the invention.

FIG. 18 is an action-timing diagram for the device of FIG. 17.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will be described next withreference to the accompanying drawings.

FIG. 1 shows a pillow-type packaging machine equipped with a transversesealing mechanism according to a first embodiment of the invention. Thispackaging machine is of the type without a filling cylinder and isstructured such that after a belt-like film S is bent into a tubularform by means of a former 2 below a hopper 1 for making bags therefrom,a pair of pull-down belts 3 each disposed therebelow with a suctionchamber 4 pulls its outer surface by the suction force to maintain it inthe cylindrical form while a longitudinal sealing is performed along itsmutually superposed longitudinal edges a by means of a longitudinalsealer 5. The film S is thereafter sent to a transverse sealer 10 to bedescribed in detail below.

The transverse sealer 10, disposed below the pull-down belts 3, is forsealing the film S in a transverse direction across the direction inwhich it is transported, and is comprised of a pair of front and backrotary arms 11 (serving as rotary driving means) for supporting a pairof transverse seal jaws 20 opposite to each other across the path oftravel of the film S such that they always face the same directions andundergo a rotary motion in synchronism with respect to each other, andpairs of left and right outer mobile frames 30 and inner mobile frames34 capable of causing the axes of rotation of the rotary arms 11 to movetowards or away from each other. The rotary arms 11 are adapted torotate such that the directions R of their rotation will match thedirection of motion A of the film S when the pair of transverse sealjaws 20 approaches each other.

As shown in FIG. 2, which is a sectional view for showing one of therotary arms 11 in detail, each rotary arm 11 is of the form of athree-sided frame with left and right arms 12 connected to each other bya connecting shaft 13. One of the arms 12 has its end section affixed toa support shaft 14 protruding inwardly from the mobile frames 30 and 34on one side (left-hand side in FIG. 2). The other of the arms 12 has itsend section affixed to a power input shaft 15 protruding inwardly fromthe mobile frames 30 and 34 on the other side (right-hand side in FIG.2). The rotary arms 11, thus structured, are adapted to be rotatedaround the shafts 14 and 15 by driving power transmitted through thepower input shaft 15.

Numerals 17 indicate sleeves which are rotatably supported around theconnecting shaft 13 and serve to support the seal jaw 20. The transverseseal jaw 20 for thermally sealing the tubularly formed film S in thetransverse direction is affixed to these sleeves 17. One of the sleeves17 is formed unistructurally with a planet gear 21.

A sun gear 24 is affixed to a fixed shaft 23 which penetrates thesupport shaft 14. The sun gear 24 and the planet gear 21 have the samenumber of gears and are coupled to each other through an idler gear 22.

Numeral 25 indicates a Schmidt coupling mechanism comprised of threedisks 25a, 25b and 25c connected through a link 26 (shown in FIG. 1).The first disk 25a of each Schmidt coupling mechanism 25 is connected toa drive shaft 27 of an arm-rotating servo motor 29 and the third disk25c of each Schmidt coupling mechanism 25 is connected to the powerinput shaft 15 such that the rotary motion of the drive shaft 27 iscommunicated to the power input shaft 15 independent of variations inthe angle of rotation or transmitted torque or any axial shift betweenthem. In this manner, the pair of rotary arms 11 can be rotated inmutually opposite directions through mutually engaging gears 28 (shownin FIG. 1) affixed on the drive shafts 27 for the Schmidt couplingmechanisms 25.

The outer and inner mobile frames 30 and 34 are for supporting the pairof rotary arms 11 such that the distance between them can be varied. Thepairs of outer and inner mobile frames 30 and 34 are respectivelyconnected to each other near the back ends by a connecting plate 31 and35 in the form of a three-sided frame surrounding the rotary arms 11.They are assembled such that the outer mobile frames 30 can slide in theforward-backward direction on a main body frame 46 and that the innermobile frames 34 can each slide inside one of the outer mobile frames 30in the forward-backward direction.

Numeral 38 indicates a turnbuckle for moving the outer and inner mobileframes 30 and 34 in the forward-backward direction in a mutuallycoordinated manner such that the transverse seal jaws 20 can be moved ina desired D-shaped trajectory including a linear section. As shown inFIG. 3, this turnbuckle 38 is axially supported by a frame structure 45provided between the outer and inner mobile frames 30 and 34. Theturnbuckle 38 has a part 38a with a right-handed screw and a part 38bwith a left-handed screw engaging respectively with the connectingplates 31 and 35 for the outer and inner mobile frames 30 and 34 throughlinear bearings 32 and 36 such that the outer and inner mobile frames 30and 34 can be moved in mutually opposite directions to cause the pair ofrotary arms 11 to move towards or away from each other by turning theturnbuckle 38 selectively in the positive or negative direction. Thelinear bearings 32 and 36 may be of a currently available type havingmany balls which engage with the screw parts 38a and 38b so as to addtorque to an arm-shifting motor 40, or to turn the turnbuckle 38 when aforce is applied to the mobile frames 30 and 34 in the forward-backwarddirection X by the reaction to the sealing pressure. The turnbuckle 38and the linear bearings 32 and 36 may together be considered to form alinear-to-rotary motion conversion means G for converting the relativemotion between the pairs of mobile frames 30 and 34 due to theaforementioned reaction to the compressive force between the pair ofseal jaws 20 into a rotary motion.

Use as the aforementioned arm-shifting motor 40, which is connected tothe turnbuckle 38 through a timing belt 39 as shown in FIG. 3, may bemade of an AC servo motor capable of freely switching betweentorque-controlled and speed-controlled modes of operation. In thetorque-controlled mode of operation, the torque of the motor 40 is keptat a specified level independent of its speed but this specified levelcan be varied suitably. In the speed-controlled mode of operation, itsrotational speed can be made constant independent of the torque. As willbe explained more in detail below, the arm-shifting motor 40 iscontrolled by a control circuit so as to be able to rotate in eitherdirection in coordination with the arm-rotating servo motor 29 forrotating the rotary arms 11 such that the transverse seal jaws 20 willeach travel in a trajectory including a straight portion of length L asshown in FIG. 5. In FIG. 1, numeral 47 indicates a partition plate.

FIG. 4 shows a circuit for controlling the arm-rotating servo motor 29and the arm-shifting servo motor 40. FIGS. 5-8 show the motion of therotary arm 11, as well as the operations of the arm-rotating andarm-shifting servo motors 29 and 40 in various modes of transversesealing operation. In FIG. 4, numeral 51 indicates a detector fordetecting the angle of rotation by the rotary arms 11 from a certainreference position I. This angle is detected from the angle of rotationof the arm-rotating servo motor 29, and a pulse signal proportional tothe angle of rotation by the rotary arms 11 is transmitted from a pulsetransmitter 52 connected to this detecting means 51 to a control unit53. Numeral 48 indicates a mode-selecting means such as a keyboard forspecifying a desired transverse sealing mode of operation. Numeral 49indicates a film-specifying means such as a key board for specifying thematerial property, thickness, width, etc. of the film. As one ofavailable transverse sealing modes, such as the "basic transversesealing mode" shown in FIG. 5, the "end acceleration mode" shown in FIG.6, the "transverse mode of operation with stripping" shown in FIG. 7, orthe "end acceleration mode with stripping" shown in FIG. 8 is specifiedthrough the mode-selecting means 48 and the material property, width,etc. of the film are specified through the film-specifying means 49, anappropriate one of programs stored in a memory means 55 is retrievedtherefrom through a retrieving means 54 and a program signal isoutputted to the control unit 53 and executed. These programs stored inthe memory means 55 are prepared for different modes of operation andaccording to different compression and distance of stroke at the time ofsealing to be explained below.

As a pulse signal from the pulse transmitter 52 and a mode-dependentprogram from the memory means 55 are inputted into the control unit 53,mode-setting means, such as those corresponding to the basic mode (53a),the end acceleration mode (53b) and the stripping mode (53c), may beactivated. The control unit 53 thereupon outputs control signals to amotor-driving means 56 in order to control the rotation of thearm-rotating servo motor 29 so as to vary the angular velocity of therotary arms 11 during the transverse sealing process, and to anothermotor-driving means 57 in order to control the timing for switching thearm-shifting servo motor 40 so as to vary the positions of the axes ofrotation of the rotary arms 11 during the transverse sealing process.The mobile frames 30 and 34, the linear-to-rotary motion conversionmeans G, the arm-shifting servo motor 40 and the control unit 53 may beregarded as constituting a trajectory-compression adjusting means H.Since the length of the transverse sealing process (that is, the strokedistance) varies as the centers of rotation of the rotary arms 11 areshifted, the remainders of the above with the linear-to-rotary motionconversion means G has been removed (that is, the mobile frames 30 and34, the arm-shifting servo motor 40 and the control unit 53) may beregarded as constituting a stroke adjusting means J.

Next, the operation of the system thus structured will be described. Letus assume first that the basic transverse sealing mode, as shown in FIG.5a with the length of transverse sealing given by L1, has been selectedthrough the mode-selecting means 48 and that material property andthickness of the film S have been specified through the film-specifyingmeans 49. In response, a program for such a basic transverse sealingmode of operation and corresponding to the specified material propertyand thickness of the film S is selected out of the many programs storedin the memory means 55 and retrieved by the retrieving means 54. Thebasic mode setting means 53a is activated according to the retrievedprogram, and the arm-shifting servo motor 40 begins to rotate in thepositive direction after the rotary arms 11 begin to rotate from thestarting position I and as they reach the starting position II for thetransverse sealing process as shown in FIG. 5a. Subsequently, thearm-shifting servo motor 40 rotates in the negative direction from themid-point III until the rotary arms 11 reach the end point IV of thetransverse sealing process so as to move the pair of rotary arms 11 awayfrom and towards each other through the outer and inner mobile frames 30and 34 engaging the turnbuckle 38. In the meantime, the film S issandwiched between the pair of transverse seal jaws 20 and moves at thesame rate as its normal speed of travel.

Accordingly, the seal jaws 20 supported at the tips of the rotary arms11 begin to travel in contact with the surface of the film S, that is,in straight lines. During this course of operation, the arm-shiftingservo motor 40 is operated in the torque-controlled mode such that itstorque is maintained at a specified constant level T₀, as shown in FIG.5b. Thus, the compressive force on the film S from the seal jaws 20 canbe kept as constant as possible. In the meantime, the arm-rotating servomotor 29 allows the speed of rotation of the rotary arms 11 to varyaccording to the torque applied thereon, causing the seal jaws 20 tomove along the film S to thereby effect the transverse sealing. Duringthis course of operation, the centers of rotation of the rotary arms 11supporting the seal jaws 20 move in the forward-backward direction X,balancing the rotary torque of the turnbuckle 38 due to the reaction tothe aforementioned compressive force against the constant torque T₀ ofthe servo motor 40 such that the compressive force is maintained at aconstant level. This constant level of the compressive force can beadjusted by varying the magnitude of T₀.

If another basic transverse sealing mode with a shorter stroke distanceL2 is specified, the arm-shifting servomotor 40 starts to rotate in thepositive direction according to the corresponding program as shown bybroken lines in FIGS. 5a and 5b, shifting the center of rotation from Oto O', and thereafter causes the seal jaws 20 to move on a shorterstraight path between points II' and IV'.

If the user specifies the end acceleration mode for causing the sealjaws 20 to accelerate and decelerate at the beginning and end of thetransverse sealing, the end acceleration mode setting means 53b isactivated. In this mode of operation, the arm-shifting servo motor 40 isgradually accelerated to gradually shift the positions of the center ofrotation of the rotary arms from O to O' as shown in FIG. 6 before thestarting point II is reached. After the end point IV is reached, themotor 40 is gradually decelerated. In other words, the program for thismode of operation provides an acceleration zone from II' to II and adeceleration zone from IV to IV' as shown in FIG. 6b. In this mode ofoperation, sudden separation of the pair of rotary arms 11 at thestarting point II of the transverse sealing, as well as sudden approachat the end point IV, can be avoided, and the transverse sealer 10 cangenerally operate more smoothly.

The stripping mode setting means 53c is activated if the user specifiesthe stripping mode of operation shown in FIG. 7 wherein the articlesinside the film S are "stripped", or caused to drop down, prior to thetransverse sealing so as not to be caught between the seal jaws 20. Inthis mode of operation, the control unit 53 causes stripping plates 61to be pressed against the film S by means of springs 60 when the rotaryarms 11 are still separated from each other (at the starting point ofstripping II') before reaching the starting point II of the transversesealing. Thereafter, the stripping plates 61 are caused to move fasterthan the film S, thereby stripping the film S until the mid-point III(the end point of stripping) is reached. At the moment, the center ofrotation of the rotary arms 11 is moved from B to C to thereby cause theseal jaws 20 to compress each other. From this moment until the endpoint IV of the transverse sealing is reached, the arm-shifting servomotor 40 is operated in the torque-controlled mode such that the sealjaws 20 are moved at the same rate as the normal speed of travel by thefilm S. With the transverse sealer 10 operated by such a program,articles to be packaged are prevented from being caught between the sealjaws 20 and the sealing operation can be accomplished dependably.

If the end acceleration mode of operation with stripping as shown inFIG. 8 is specified, the sealer 10 is operated with a program providingan acceleration zone from II' to II before the starting point of thestripping and a deceleration zone from IV to IV' after the end point IVfor the transverse sealing.

As explained above by way of the embodiments described above withreference to FIGS. 1-8, transverse sealing can be performed on acontinuously moving film S because the pair of sealing jaws 20 (servingas transverse sealing means) is caused to travel in a linear trajectoryalong the path of the film S by the aforementionedtrajectory-compression adjusting means H. Since the compressive forcebetween the pair of seal jaws 20 can be maintained at a constant levelcorresponding to a set magnitude of torque T₀ on the arm-shifting servomotor 40, the film S can be transversely sealed appropriately accordingto its thickness, material property, etc. Since the stroke distance, andhence the time duration of the sealing operation, can be selectedappropriately by the stroke adjusting means J according to the thicknessand material property of the film S, the sealing operation can beperformed even more appropriately according to the present invention.

Since the aforementioned trajectory-compression adjusting means H hasboth the function of moving the pair of seal jaws 20 in a desiredtrajectory and the function of maintaining the compression therebetweenat a constant level, the sealer 10 as a whole can be more simplystructured than if these two functions are performed by two separatemechanisms. Since the motor 40 takes the place of a hydraulic cylinder,furthermore, the sealer can be made more compact and the possibility ofcontamination of the articles to be packaged by oil can be eliminated.The sealer 10 according to the present invention can be made compactalso because the pairs of outer and inner mobile frames 30 and 34, thearm-shifting servo motor 40 and its control unit 53, which constitute aportion of the aforementioned trajectory-compression adjusting means H,also serve as the aforementioned stroke adjusting means J. Instead ofthe aforementioned linear-to-rotary motion conversion means G with aturnbuckle and linear bearings, use may also be made of an alternativemechanism with a link mechanism or groove cams.

FIG. 9 shows a second embodiment of the present invention characterizedwherein the supporting mechanism for the seal jaws 20 is improved byadding a returning means. As shown in FIG. 9, wherein the samecomponents as described above are indicated by the same numerals, thebase ends of support springs 71 (serving as returning means) areattached to the inner edges of the pair of sleeves 17 rotatablysupported by the connecting shaft 13 between the arms 12. These springs71 are cantilevered and are for the purpose of applying a uniformcompressive force to the film S over its entire width W. Their free endsextend inwardly toward each other and are attached to a seal jaw 20.

With the returning means 71 thus provided, even if the seal jaws 20become sloped like a seesaw because of the longitudinally sealed edgeportions of the film S caught in between as the seal jaws 20 are pressedagainst each other, these support springs 71 will individually bend andsupply a restoring force proportional to its strain to cause the sealjaw 20 attached thereto to return towards the opposite seal jaw 20,thereby applying a uniform compressive force onto the film S.

As the pair of seal jaws 20 moves in D-shaped trajectories by therotation of the arms 12 of the rotary arms 11 and the motion of themobile frames 30 and 34 and reaches the starting point of the transversesealing, coming into contact with each other with the film S sandwichedtherebetween, the seal jaws 20 experience a force which tend to movethem around the longitudinally sealed edges of the film S. When such aforce is experienced by the seal jaws 20, each of the support springs 71is bent according to the displacement of the seal jaw 20. At the sametime, reactions from the support springs 71 are applied back onto theseal jaws 20 so as to press the film S uniformly to perform thetransverse sealing.

This process will be explained more in detail with reference to FIG. 10which shows the pair of seal jaws 20 sandwiching therebetween a film Shaving its longitudinally sealed edges a formed in three or four layers.In this situation, at least one of the pair of seal jaws 20 will assumea sloped position like a seesaw around the longitudinally sealed edgesa. This slope can be expressed as a function of the strains of thesprings 71. The strain δ is given by a formula as follows:

    δ=pA.sup.3 /12EI=pD.sup.3 /Ebt.sup.3                 (1)

where D is the effective length of the cantilevered support spring 71, tis the thickness and b is the width of the plate of the spring, 2p isthe load, and E and I are respectively the Young's modulus and thesecond-order cross-sectional moment of the spring 71. Its reaction forceR is inversely proportional to the strain δ and given by

    R=Ebt.sup.3 δ/D.sup.3.                               (2)

Thus, if the strain of the left-hand and right-hand support springs 71is respectively δ_(l) and δ_(r), their reaction forces R_(l) and R_(r)proportional respectively to δ_(l) and δ_(r) are applied to the seal jaw20 towards the other seal jaw 20 opposite thereto.

Consider, for example, a load of 500 kg applied to a support spring 71of effective length D=44 mm, plate thickness t=5 mm, plate width b=18mm, and Young's modulus=2.1×10⁴ kg/mm², thereby causing a strain of 0.5mm and 0.4 mm to the left-hand and right-hand springs 71, respectively.Formula (2) then shows that the support spring 71 on the left-hand sideexerts a reaction force of R_(l) =278 kg to the seal jaw 20 and that thesupport spring 71 on the right-hand side exerts a reaction force ofR_(r) =222 kg in the direction of returning to the normal position,providing locally uniform compression to the film S and restoring thestrains in the springs 71.

FIG. 11 shows a support spring of a different form. A seal jaw 20Aaccording to this embodiment has an inwardly extending slit 72 formedfrom each side section thereof, and the parts which become separated bythese slits 72 from the main part of the seal jaw 20A are formed ascantilevered elastic support spring parts 73.

FIG. 12 shows a support spring of still another form. A seal jaw 20Baccording to this embodiment is formed as a hollow structure with anelastic hollow housing structure 200 such that the strain of the sealjaw 20B will be made up for by a reaction force proportional to thebending of the housing structure 200 itself. A fluid 75 with a lowmelting point such as lead may be sealed inside the hollow interior 74of the housing structure 200 for providing a uniform thermal balance tothe seal jaw 20B. In such a situation, the housing structure 200 servesas the aforementioned returning means. The support springs 71 and 73 andthe hollow elastic structure 20B may be used only as one of the pair ofseal jaws 20.

FIG. 13 shows still another transverse sealer according to a thirdembodiment of the invention. This sealer has both a seal jaw 20 and astripping plate 61 provided at the tip of each rotary arm 11 such thatthe stripping plate 61 performs the stripping operation on the film Swhile the seal jaw 20 is on the first half of the straight linetrajectory from I to III and the transverse sealing is carried out whilethe seal jaw 20 is on the second half of this trajectory.

Explained more in detail, means for allowing the seal jaws 20 to move inmany different D-shaped trajectories having linear sections of differentlengths (or many different stroke distances), or means for shifting theaxes of rotation of the rotary arms 11 according to this embodiment ofthe invention comprises two cams 84A and 84B having different guidesurfaces affixed to the same axis such that they rotate together andtheir rotary positions can be adjusted. At the same time, one or both ofthe cam axes 85 (only the one on the right-hand side according to theembodiment shown in FIG. 13) are subjected to a biasing force towardsthe other by means of an air cylinder 86 such that the pair of seal jaws20 can apply an appropriate pressure on the film S while they areperforming transverse sealing between the points II and III.

The air tube connecting the air cylinder 86 with an air supply source 87is provided with an electromagnetic valve 88 which opens the air supplyroute only during the transverse sealing process between the points IIand III and an external pilot type sequence valve 89 which is activatedonly when the contact pressure exceeds a set level such that thetransverse sealing can be effected at a constant contact pressure. Onthe other hand, the arm-rotating servo motor is controlled so as torotate at an increased speed during the stripping process between thepoints I and II. In this manner, the stripping can be completed quicklybefore the transverse sealing process is started.

In summary, the third embodiment of the invention makes use of thearm-rotating servo motor and arm-shifting cams 84A and 84B incoordination therewith such that the rotary arms 11 are separated fromeach other by the operation of these cams 84A and 84B while the sealjaws 20 are in the region for stripping operation between the points Iand II and the air cylinder 86 is not operated. In the meantime, thespeed of rotation of the arm-rotating servo motor is increased such thatthe stripping plates 61 will move in a straight trajectory faster thanthe normal speed of travel of the film S so as to effect requiredstripping thereon. When the seal jaws 20 start the transverse sealingprocess to be effected between the points II and III, the arm-rotatingservo motor is rotated at a constant speed and the electromagnetic valve88 is opened so as to introduce air into the air cylinder 86 through theexternal pilot type sequence valve 89. In this manner, an appropriatecompressive force according to the thickness and material property ofthe film S is applied between the seal jaws 20 as the arm-shifting cams84A and 84B are pressed towards the other cams 84A and 84B on theopposite side.

The stripping process between the points I and II is controlled by oneof the pairs of cams 84B, while the transverse sealing process betweenthe points II and III is controlled by the other pair of cams 84A. Thus,the stroke distances of these two processes I-II and II-III can bevaried by controlling the motion of the cams 84A and 84B. These pairs ofcams 84A and 84B, however, may be replaced by different means such asair cylinders for shifting the axes of rotation.

FIG. 14 shows still another transverse sealer according to a fourthembodiment of the present invention characterized as having a shiftingmeans K for shifting the positions of the rotary arms 11 supporting theseal jaws 20 in the direction of motion of the film S by a specifiedstroke distance during the transverse sealing process. A pair of sideboards 91 and 92 is provided to hold the base parts of the rotary arms11 and is connected to each other by a pair of connecting boards 93 and94 to form a mobile frame 90 surrounding the rotary arms 11 and adaptedto slide vertically upward and downward, guided by four guide rods 95provided to the main body frame 46. Numeral 96 indicates a driving motor(or an arm-raising motor) for moving the mobile frame 90 upwards anddownwards for moving the seal jaws 20 in elliptical trajectories of aspecified shape. An AC servo motor capable of changing the direction ofrotation at a specified timing may be used as this driving motor 96. Theaforementioned shifting means K may be regarded as consisting of themobile frame 90, the guide rods 95 and the driving motor 96. Every timethe seal jaws 20 come near the mutually contacting positions or the mostdistantly separated positions, a control unit to be described belowcauses the driving motor 96 to rotate in the positive or negativedirection to thereby move the rotary arms 11 upward or downward by aspecified distance through a bracket 98 on the mobile frame 90 engaginga screw bar 97 serving as the drive shaft of the driving motor 96. Theother components shown in FIG. 14 are the same as those shown in FIG. 1and hence are indicated by the same numerals.

FIG. 15 shows a circuit for controlling the arm-rotating motor 29 andthe arm-raising motor 96, and FIG. 16 is for showing the movement of therotary arms 11 by their coordinated operations. Numeral 101 in FIG. 15indicates a detector for detecting the angle of rotation by the rotaryarms 11 from a certain reference position I. This angle is detected fromthe angle of rotation of the arm-rotating motor 29, and a pulse signalproportional to the angle of rotation by the rotary arms 11 istransmitted from a pulse transmitter 102 connected to this detectingmeans 101 to a control unit 103. Numeral 100 indicates a film-specifyingmeans such as a key board for specifying the material property, width,thickness, etc. of the film. If the width of the film, etc. arespecified, a retrieving means 104 is activated and retrieves acorresponding program out of many stored in a memory 105, outputting itto the control unit 103 to have it carried out. When the pulse signalfrom the pulse transmitter 102 and a signal from the film-specifyingmeans 100 are received, the control unit 103 outputs a control signal tothe motor-driving means 106 to control the rotary motion of thearm-rotating motor 29 so as to vary the angular speed of the rotary arms11 during the course of transverse sealing. At the same time, wheneverthe rotary arms 11 reach the transverse sealing zone II-II' or thecorresponding zone IV-IV' in their upward trajectory with reference toFIG. 16, a control signal is outputted to another motor-driving means107 to control the switching timing of the arm-raising motor 96 so as torotate this motor 96 by an angle corresponding to a specified strokedistance L. The aforementioned shifting means K and the control unit 103together may be regarded as constituting the stroke adjusting means J.

Next the operation of the sealer thus structured will be explained. Tostart, the material property, thickness and/or width of the film S isspecified through the film-specifying means 104. In response, thearm-raising motor 96 starts to rotate in the positive directionaccording to a preliminarily retrieved program when the rotary arms 11,starting its motion from the preliminarily determined starting point I,reaches the starting points II for the transverse sealing. The mobileframe 90 is thereby lowered at the same speed as that of the film S inits direction of motion A by a distance of stroke L determined by thematerial property, etc. of the film S. As a result, the seal jaws 20supported by the rotary arms 11 begin to move downward in contact withthe film S over a stroke distance L determined by the specified width,material property or thickness of the film S, while the arm-rotatingmotor 29 increases and/or decreases its rotational speed according tothe variation on its torque, so as to carry out the transverse sealing.When the transverse sealing is completed at the end points II', the sealjaws 20 continue to rotate further and when they reach the points IVwhere they are farthest apart on their trajectories, the arm-raisingmotor 96 begin to rotate in the negative direction according to theprogram, raising the rotary arms 11 upwards back to their startingpositions.

The fourth embodiment of the invention is advantageous because the sealjaws 20 each move in a relatively simpler trajectory made of a circulararc and a straight line segment instead of a D-shaped trajectory as inthe case of the third embodiment of the invention. As a result, controlof the motion is simpler.

Although the fourth embodiment of the invention was described above asusing the screw bar 97 of the arm-raising motor 96 in order to raise andlower the mobile frame 90 and the rotary arms 11, other mechanisms forraising and lowering the mobile frame 90 may be substituted if capableof varying the stroke distance L of the mobile frame 90 according to thematerial property, etc. of the film S, such as a mechanism with a rackand a pinion. If necessary, furthermore, a sealer according to thefourth embodiment of the invention may be controlled such that therewill be no relative motion between the seal jaws 20 and the film Sthroughout the distance between the points II and II' by stopping thearm-rotating motor 29 while the arm-raising motor 96 is operating.

The first through fourth embodiments of the present invention describedabove relate to transverse sealers of the type causing seal jaws to movein generally circular trajectories such that the transverse sealing canbe effected while the film S is being transported. In contrast, FIG. 17shows a fifth embodiment of the present invention related to atransverse sealer 10A of the intermittent driving type characterized asstopping the transportation of the film S intermittently and carryingout the transverse sealing only while the film S is temporarily stopped.

With reference to FIG. 17, the transverse sealer 10A according to thefifth embodiment of the invention supports its seal jaws 20 directly bythe outer and inner mobile frames 30 and 34 without using any rotaryarms. Thus, the pair of seal jaws 20 can be moved towards or away fromeach other by means of a jaw-shifting servo motor 40A such that the filmS is sandwiched between them and the transverse sealing can be effectedwhile the seal jaws 20 are in their mutually approached condition. Theprinciple of mechanism for moving the seal jaws towards and away fromeach other is the same as that explained above with reference to FIG. 3.With reference still to FIG. 17, the linear-to-rotary motion conversionmeans G comprised of the pairs of outer and inner mobile frames 30 and34, the turnbuckle 38 and the linear bearings 32 and 36, and thejaw-shifting servo motor 40A together may be regarded as constituting acompression-adjusting means H1.

As shown in FIG. 18, the jaw-shifting servo motor 40A according to thefifth embodiment of the invention rotates in the positive direction fromtime t₁ when the pair of seal jaws 20 is farthest apart from each otheruntil time t₂ when it comes in contact with the film S to advance theseal jaws 20 in the positive direction. In the meantime, the motor 40Ais operated in the speed-controlled mode such that its rotational speedwill remain constant independent of changes in its torque. During thesealing process from time t₂ until time t₃, the servo motor 40A iscontrolled to produce a specified torque T₀. Since the rotary torque ofthe turnbuckle 38 shown in FIG. 17 due to the reaction force to thecompression between the seal jaws 20 is applied to the servo motor 40Ain this situation, the servo motor 40A stops when the aforementionedrotary torque of the turnbuckle 38 is greater than the specified torqueT₀ of the servo motor 40A but the servo motor 40A turns in the positiveor negative direction, when the rotary torque of the turnbuckle 38 issmaller than T₀, so that the compression between the seal jaws 20 willbe adjusted corresponding to the specified torque T₀.

Thus, when a thermal sealing process is carried out with a packagingmachine of an intermittent driving type while the film S is temporarilystopped, the compression force between the pair of seal jaws 20 can bemaintained at a specified level by means of the aforementionedcompression-adjusting means H1. As a result, the transverse sealingprocess can be appropriately carried out on a film according to itsthickness, material property, and width. Since use is made of a motorinstead of a hydraulic cylinder, the sealer can be made compact andthere is no possibility of contamination of the articles by oil. It nowgoes without saying that returning means of types similar to those shownat 71, 73 and 200 as shown in FIGS. 9-12 may be provided to the sealjaws 20 of this fifth embodiment of the invention.

Although the first through fifth embodiments of the present inventiondescribed above all relate to a transverse sealer to be used in apackaging machine of a vertical pillow type, it should be clear that thetransverse sealer according to the present invention can be used also ina horizontal pillow type packaging machine. In addition, the transversesealers of the present invention can also be used with a packagingmachine of a three-side sealing type adapted to fold the film into two,to vertically seal its superposed edges longitudinally and then totransversely seal it at two places or of a four-side sealing typeadapted to perform a vertical sealing at two places along the superposededges and also along the opposite side and then to perform transversesealing at two places.

It also goes without saying that the present invention is applicable notonly to machines for packaging food articles but also to packagingmachines for industrial parts or products.

What is claimed is:
 1. A transverse sealer for a packaging machine forsealing a bag in a transverse direction after said bag is filled witharticles to be packaged, said bag being made from a belt-like elongatedfilm moving on a transportation path in an film-transporting direction,said transverse direction being transverse to said film-transportingdirection, said transverse sealer comprising:a pair of transversesealing means disposed downstream to bag-forming means for transformingsaid film into a specified shape for forming a bag and opposite to eachother on mutually opposite sides of said transportation path of saidfilm; a pair of rotary driving means for causing said pair of transversesealing means to rotate in synchronism with each other such that saidtransverse sealing means move along said film-transporting directionwhen said transverse sealing means are near each other; and atrajectory-compression adjusting means for causing said pair oftransverse sealing means to move on straight trajectories along saidtransportation path of said film by causing said pair of rotary drivingmeans to move towards and away from each other and maintaining acompressive force between said pair of transverse sealing means at aspecified level while said pair of rotary driving means causes said pairof transverse sealing means to sandwich and compress said filmtherebetween.
 2. The transverse sealer of claim 1 further comprising astroke adjusting means for adjusting the distance of stroke by saidtransverse sealing means along said straight trajectories.
 3. Thetransverse sealer of claim 1 wherein said trajectory-compressionadjusting means includes:a pair of mobile frames which are movable in anapproach-separation direction in which said pair of transverse sealingmeans moves towards and away from each other, each supporting one ofsaid pair of rotary driving means, and receiving the reaction of saidcompressive force; a linear-to-rotary motion conversion means forconverting the relative motion between said pair of mobile frames due tosaid reaction into a rotary motion; an approach-separation motor forcausing said pair of mobile frames in said approach-separation directionthrough said linear-to-rotary motion conversion means; and a controlmeans for causing said approach-separation motor to rotate at aspecified torque to thereby cause said pair of transverse sealing meansto travel in specified trajectories including said straighttrajectories.
 4. The transverse sealer of claim 2 wherein said strokeadjusting means includes:a pair of mobile frames, said mobile framesbeing movable in an approach-separation direction in which said pair oftransverse sealing means move towards and away from each other, and saidmobile frames each supporting one of said pair of rotary driving means;an approach-separation motor for causing said pair of mobile frames tomove in said approach-separation direction; and a control means forcontrolling said approach-separation motor to thereby cause said pair oftransverse sealing means to travel in specified trajectories includingsaid straight trajectories having a specified length.
 5. The transversesealer of claim 2 wherein said stroke adjusting means includes ashifting means for moving said pair of rotary driving means by aspecified distance along said film-transporting direction when saidtransverse sealing means have rotatingly reached starting positions oftransverse sealing.
 6. The transverse sealer of claim 5 wherein saidshifting means include:a mobile frame which is movable in saidfilm-transporting direction and supports said pair of rotary drivingmeans; and an arm-raising motor for moving said mobile frame in saidfilm-transporting direction.
 7. The transverse sealer of claim 1 whereinsaid trajectory-compression adjusting means include a acceleration-modesetting means for causing said pair of rotary driving means to graduallymove away from each other before said pair of transverse sealing meansreaches starting positions of transverse sealing and to gradually movetoward each other after said pair of transverse sealing means reachesend positions of said transverse sealing.
 8. The transverse sealer ofclaim 1 wherein each of said transverse sealing means has a sealingsurface for contacting said film and includes a stripping plateprotruding further towards said film than said sealing surface, and saidtrajectory-compression adjusting means includes a stripping-mode settingmeans for causing said film to be sandwiched between the pair of saidstripping plates before the sealing surfaces of said pair of transversesealing means reach starting positions of transverse sealing and tostrip said film by causing said pair of transverse sealing means to movefaster than said film while said film remains sandwiched between saidstripping plates.
 9. The transverse sealer of claim 1 wherein at leastone of said pair of transverse sealing means has attached thereto areturning means for pressing said one transverse sealing means in thedirection towards the other of said pair of transverse sealing means bya restorative elastic force proportional to the strain of said returningmeans.
 10. A transverse sealer for a packaging machine for sealing a bagin a transverse direction after said bag is filled with articles to bepackaged, said bag being made from a belt-like elongated film moving ona transportation path in an film-transporting direction, said transversedirection being transverse to said film-transporting direction, saidtransverse sealer comprising:a pair of transverse sealing means disposeddownstream to bag-forming means for transforming said film into aspecified shape for forming a bag and opposite to each other on mutuallyopposite side of said transportation path of said film; and acompression adjusting means both for moving said pair of transversesealing means in an approach-separation direction towards and away fromeach other to thereby sandwich said film at a specified seal positionthereon for thermal sealing and for maintaining a compressive forcebetween said pair of transverse sealing means at a specified level; saidcompression adjusting means comprising: a pair of mobile frames whichare movable in an approach-separation direction in which said pair oftransverse sealing means moves towards and away from each other, eachsupporting one of said transverse sealing means and receiving thereaction force to said compressive force; a linear-to-rotary motionconversion means for converting the relative motion between said pair ofmobile frames due to said reaction force into a rotary motion; and aframe-moving motor for moving said pair of mobile frames towards andaway from each other in said approach-separation direction through saidlinear-to-rotary motion conversion means.
 11. The transverse sealer ofclaim 10 wherein at least one of said pair of transverse sealing meanshas attached thereto a returning means for pressing said one transversesealing means in the direction towards the other of said pair oftransverse sealing means by a restorative elastic force proportional tothe strain of said returning means.
 12. A transverse sealer for apackaging machine for sealing a bag in a transverse direction after saidbag is filled with articles to be packaged, said bag being made from abelt-like elongated film moving on a transportation path in anfilm-transporting direction, said transverse direction being transverseto said film-transporting direction, said transverse sealer comprising:apair of transverse sealing means disposed downstream to bag-formingmeans for transforming said film into a specified shape for forming abag and opposite to each other on mutually opposite sides of saidtransportation path of said film; a pair of rotary driving means forcausing said pair of transverse sealing means to rotate in synchronismwith each other such that said transverse sealing means move along saidfilm-transporting direction when said transverse sealing means are neareach other; and a trajectory-compression adjusting means for causingsaid pair of transverse sealing means to move on straight trajectoriesalong said transportation path of said film by causing said pair ofrotary driving means to move towards and away from each other andmaintaining a compressive force between said pair of transverse sealingmeans at a specified level while said transverse sealing means and saidfilm move continuously along said transportation path and said pair ofrotary driving means causes said pair of transverse sealing means tosandwich and compress said film therebetween.
 13. The transverse sealerof claim 12 further comprising a stroke adjusting means for adjustingthe distance of stroke by said transverse sealing means along saidstraight trajectories.
 14. The transverse sealer of claim 12 whereinsaid trajectory-compression adjusting means includes:a pair of mobileframes which are movable in an approach-separation direction in whichsaid pair of transverse sealing means moves towards and away from eachother, each supporting one of said pair of rotary driving means, andreceiving the reaction of said compressive force; a linear-to-rotarymotion conversion means for converting the relative motion between saidpair of mobile frames due to said reaction into a rotary motion; anapproach-separation motor for causing said pair of mobile frames in saidapproach-separation direction through said linear-to-rotary motionconversion means; and a control means for causing saidapproach-separation motor to rotate at a specified torque to therebycause said pair of transverse sealing means to travel in specifiedtrajectories including said straight trajectories.
 15. The transversesealer of claim 13 wherein said stroke adjusting means includes:a pairof mobile frames, said mobile frames being movable in anapproach-separation direction in which said pair of transverse sealingmeans move towards and away from each other, and said mobile frames eachsupporting one of said pair of rotary driving means; anapproach-separation motor for causing said pair of mobile frames to movein said approach-separation direction; and a control means forcontrolling said approach-separation motor to thereby cause said pair oftransverse sealing means to travel in specified trajectories includingsaid straight trajectories having a specified length.
 16. The transversesealer of claim 13 wherein said stroke adjusting means includes ashifting means for moving said pair of rotary driving means by aspecified distance along said film-transporting direction when saidtransverse sealing means have rotatingly reached starting positions oftransverse sealing.
 17. The transverse sealer of claim 16 wherein saidshifting means include:a mobile frame which is movable in saidfilm-transporting direction and supports said pair of rotary drivingmeans; and an arm-raising motor for moving said mobile frame in saidfilm-transporting direction.
 18. The transverse sealer of claim 12wherein said trajectory-compression adjusting means include aacceleration-mode setting means for causing said pair of rotary drivingmeans to gradually move away from each other before said pair oftransverse sealing means reaches starting positions of transversesealing and to gradually move toward each other after said pair oftransverse sealing means reaches end positions of said transversesealing.
 19. The transverse sealer of claim 12 wherein each of saidtransverse sealing means has a sealing surface for contacting said filmand includes a stripping plate protruding further towards said film thansaid sealing surface, and said trajectory-compression adjusting meansincludes a stripping-mode setting means for causing said film to besandwiched between the pair of said stripping plates before the sealingsurfaces of said pair of transverse sealing means reach startingpositions of transverse sealing and to strip said film by causing saidpair of transverse sealing means to move faster than said film whilesaid film remains sandwiched between said stripping plates.
 20. Thetransverse sealer of claim 12 wherein at least one of said pair oftransverse sealing means has attached thereto a returning means forpressing said one transverse sealing means in the direction towards theother of said pair of transverse sealing means by a restorative elasticforce proportional to the strain of said returning means.